PROJECT SUMMARY/ABSTRACT A growing body of evidence suggests that growth factors (GFs), once considered to function mainly in development, also regulate synaptic plasticity and memory in the adult. This proposal reflects on an ongoing research program in our laboratory that has focused on the role of GFs in memory formation. The primary focus of this current project is to examine GF-mediated memory formation from a novel perspective, which takes into account the temporal aspect of their activity as part of the cellular computation involved in forming memories. Repeated-trial learning, a fundamental form of memory acquisition exhibited by virtually all animals, including man, requires a temporal interaction between an ongoing stimulus and the delayed effects of a previous stimulus. We will use a powerful paradigm to study repeated-trial training in the marine mollusk Aplysia, which develops long-term memory (LTM) for sensitization after only two training trials, but only if they are separated by a permissive and surprisingly specific time interval of ~45 min. This minimal system clearly separates the initiating stimulus (Trial 1) from the repeated stimulus (Trial 2), providing unparalleled access to the temporal interactions underlying repeated-trial LTM. We will investigate two GF-dependent mechanisms that our preliminary evidence suggests contribute significantly to temporal processing at the heart of repeated-trial learning. The first (explored in AIM 1) is a distributed mechanism for GF-dependent phosphorylation of extracellularly regulated kinase (ERK). The second mechanism (explored in AIM 2) is the multi-step signaling of a specific GF, TGF?, which we propose similarly integrates the timing of training trials. Finally, in AIM 3 we will try to establish causal connections between the timing of single ERK phosphorylation, TGF? availability, and the persistent effects of two-trial training The project holds promise for significant impact from both a basic scientific perspective and a clinical perspective. From a basic scientific perspective, Aplysia provides an exceptional experimental system that has the potential to demonstrate causal linkages between GF-mediated memory formation and its underlying synaptic and molecular mechanisms, while simultaneously exploring the temporal features of those mechanisms. And from a clinical perspective, the impact of this project addresses a major challenge in mental health: to understand and treat the devastating cognitive disorders that accompany neurodegenerative diseases. GF signaling has been directly implicated in many of these diseases and, since GFs are extracellular proteins, understanding when and where they act in the brain during memory formation could provide novel strategies for developing more specific and more effective therapeutic agents.